1. Field of the Invention
The present invention relates to an ink cartridge for ink jet use having an aperture serving as an opening for ink filling, which is sealed, and the invention relates to a method for sealing such aperture.
2. Related Background Art
As an ink cartridge suitable for use in the technical field of ink jet printing, the one having a structure shown in FIGS. 3A to 3C is known, for example. FIG. 3A is a cross-sectional view showing such ink cartridge. FIG. 3B is an enlarged sectional view showing the ink filling opening thereof. FIG. 3C represents FIG. 3B, observed from below in the direction indicated by an arrow in FIG. 3B.
In FIG. 3A, a reference numeral 300 designates an ink cartridge formed by polypropylene (PP) or the like, for example. The ink cartridge 300 substantially comprises a container 302 for a member that generates negative pressure, which is partitioned by a partitioning wall 301, and an ink container 303. The container 302 for a member that generates negative pressure and the ink container 303 are conductively connected through a conductive aperture 304. For the container 302 for a member that generates negative pressure, an ink supply port 305 is formed to supply ink to an ink jet head (not shown) that can be mounted on an ink cartridge. On one wall of the container 302 for a member that generates negative pressure, where the ink supply port 305 is formed, an air conduit hole 305 is arranged away from the ink supply port. In the interior of the container 302 for a member that generates negative pressure, a negative pressure generating member 307 formed by a porous element or the like is contained to absorb and hold ink, while ink is contained directly in the interior of the ink container arranged adjacent to it. For this ink container 303, an ink filling port 309 is formed as an aperture to fill in the container with ink directly.
As shown in FIG. 3D, the ink filling port 309 substantially comprises a recessed portion 309a where a plug, to be described later, is inserted under pressure to airtightly close the ink filling port 309; and an aperture 309b formed on the bottom of the recessed portion 309a and arranged to be conductively connected with the ink container 303. A plug 310 that can be inserted into the recessed portion 309a is usually a metallic ball of SUS or the like or a plastic ball of PP or the like. Then, a ball of the kind is inserted into the ink filling port 309 under pressure after the ink container is filled with ink, thus keeping the ink filling port in a state of being sealed.
Ink is filled into the ink cartridge structured as described above from the aperture 309b of the ink filling port 309. As a method therefor, it is possible to adopt any one of the known methods, such as applying pressure or reducing pressure, among others.
After ink is filled, ink cartridges are often distributed on the market individually. In this case, all the apertures of the ink cartridge including the ink filling port 309 (and the ink supply port 305 and the air conduit hole 306, for example) should be closed by sealing material as a preventive measure against the evaporation of ink and the expansion of air in the container. (Here, the ink filling port 309 is sealed by the plug 310 as described above.)
As a sealing material to be used preferably for closing such apertures as described above, it is possible to use a compound material produced by combining a single layered barrier, which is called a "barrier material" in the field of packaging industry, and a multi-laminated plastic film, or a compound barrier material produced by combining this compound material and a reinforcing material, such as paper or fabrics or by combining it with aluminum foil or the like. Particularly, using the same material as that of an ink cartridge as an adhesive layer, it becomes possible to maintain a higher airtightness when the sealing material is thermally welded to the ink supply port 305, and the air conduit hole 306, which also provide apertures for an ink cartridge.
As described above, the ink filling port 309, ink supply port 305, and air conduit hole 306 are airtightly sealed. Therefore, there is no ink leakage or the like, and extremely high reliability is obtainable when the ink cartridge 301 is distributed on the market individually.
Now, in this respect, the SUS ball used for pressurized insertion to the ink filling port of an ink cartridge of the kind is prepared for the intended process only after a severe selection so that the acceptable ball should have no scratches or cracks on the surface or any other defects. Therefore, it is required to take many steps when selecting the balls, leading to a disadvantage that the costs become inevitably high. Also, the SUS balls, which are made available after a severe selection process, may sometimes present the scratches or cracks that cannot be discriminated by eye-sight. If such SUS balls should be used, it is conceivable that the provision of any perfect durability is hindered or there may be produced ink tanks, which are unable to fit for use in the environments subjected to changes. A problem that scratches and the others cannot be discriminated perfectly by eye-sight is equally encountered when using PP balls. The scratches and others may exist in the interior of the ink filling port, too.
Here, the following is regarded as causes of the generation of these scratches and others:
As the causes of scratches in the interior of the ink filling port are:
1) Welded lines created when forming an ink tank.
2) Scratches created by rubbing when the ink filling port is being pressed by the ink filling mouth of an ink filling machine.
Also, for the causes of scratches on the surface of the plug:
1) Scratches created by rubbing of one plug with another when being distributed on the market.
2) Welded lines created when forming a plug.
If a plug having such scratches and others is pressed in the ink filling port described above, ink may leak from the ink filling port or it becomes impossible to keep the ink container airtightly closed. As a result, the performance of an ink cartridge cannot be anticipated as desired, and then, conceivably, ink is caused to shift into a negative pressure generating member in the container for such member. Therefore, ink may leak from the ink supply port. In order to prevent such ink cartridge from being distributed on the market, it should be necessary to exercise an inspect by leaving the ink tank for a period of 8 to 24 hours with the ink filling port being placed downward after the ink filling port, ink supply port, and air conduit hole are sealed or to adopt an inspection method in which the ink tank is left in a dry preservation equipment at 45.degree. C. or at 60.degree. C. With an inspection of the kind, ink leakage from the ink filling port is noticed if any fine leakage takes place in the ink filling port or a phenomenon is observable that the portion of the negative pressure generating member, which is not wet by ink usually, is wet by ink sucked up by means of capillary force of the negative pressure generating member. Thus, those cartridge presenting ink leakage can be checked and excluded while still in the manufacturing stage. However, the execution of these inspecting steps to find ink leakage from the ink filling port not only results in the elongated production tact, but also, results in the reduced yield due to the defective products thus excluded. The costs of manufacture rises inevitably.
Therefore, it has been studied to apply a thermal welding method to a PP ball after it is pressed in the filling port for sealing it. However, with the usual thermal welding method, heat cannot be concentrated in the vicinity of the ink filling port for the intended thermal welding. The heat tends to affect the other portions of the ink cartridge, leading to the thermal influence exerted on the ink that has been contained. Also, there is a possibility that an adverse effect is produced on the reliability of the airtightness of the ink tank itself eventually.